Synthesis of 4-styrylpyrazoles and Evaluation of their Inhibitory Effects on Cyclin-dependent Kinases

Cycle-regulating and transcriptional cyclin-dependent kinases (CDKs) are attractive targets in cancer drug development. Several CDK inhibitors have already been obtained or are close to regulatory approval for clinical applications.

Phenylazopyrazole CAN508 has been described as the first selective CDK9 inhibitor with an IC50 of 350 nM. Since the azo-moiety is not a suitable functionality for drugs due to pharmacological reasons, the preparation of carbo-analogues of CAN508 with similar biological activities is desirable. The present work is focused on the synthesis of carbo-analogues similar to CAN508 and their CDK inhibition activity.

Herein, the synthesis of 21 novel carbo analogues of CAN508 and their intermediates is reported. Subsequently, target compounds 8a - 8u were evaluated for protein kinase inhibition (CDK2/cyclin E, CDK4/cyclin D, CDK9/cyclin T) and antiproliferative activities in cell lines (K562, MCF-7, MV4-11). Moreover, the binding mode of derivative 8s in the active site of CDK9 was modelled.

Compounds 8a - 8u were obtained from key intermediate 7, which was prepared by linear synthesis involving Vilsmeier-Haack, Knoevenagel, Hunsdiecker, and Suzuki-Miyaura reactions. Styrylpyrazoles 8t and 8u were the most potent CDK9 inhibitors with IC50 values of approximately 1 μM. Molecular modelling suggested binding in the active site of CDK9. The flow cytometric analysis of MV4-11 cells treated with the most active styrylpyrazoles showed a significant G1-arrest.

The prepared styrylpyrazoles showed inhibition activity towards CDKs and can provide a novel chemotype of kinase inhibitors.